On the read back by the FDC, the controller must begin synchronization at the beginning of the sync field. For the
conventional mode, the internal PLL VCO is enabled (VCOEN) approximately 24 bytes from the start of the Gap2 field.
But, when the controller operates in the 1 Mbps perpendicular mode (WGATE = 1, GAP = 1), VCOEN goes active after
43 bytes to accommodate the increased Gap2 field size. For both cases, and approximate two-byte cushion is
maintained from the beginning of the sync field for the purposes of avoiding write splices in the presence of motor speed
variation.
For the Write Data case, the FDC activates Write Gate at the beginning of the sync field under the conventional mode.
The controller then writes a new sync field, data address mark, data field, and CRC. With the pre-erase head of the
perpendicular drive, the write head must be activated in the Gap2 field to insure a proper write of the new sync field. For
the 1 Mbps perpendicular mode (WGATE = 1, GAP = 1), 38 bytes will be written in the Gap2 space. Since the bit density
is proportional to the data rate, 19 bytes will be written in the Gap2 field for the 500 Kbps perpendicular mode (WGATE =
1, GAP =0).
It should be noted that none of the alterations in Gap2 size, VCO timing, or Write Gate timing affect normal program
flow. The information provided here is just for background purposes and is not needed for normal operation. Once the
Perpendicular Mode command is invoked, FDC software behavior from the user standpoint is unchanged.
The perpendicular mode command is enhanced to allow specific drives to be designated Perpendicular recording drives.
This enhancement allows data transfers between Conventional and Perpendicular drives without having to issue
Perpendicular mode commands between the accesses of the different drive types, nor having to change write pre-
compensation values.
When both GAP and WGATE bits of the PERPENDICULAR MODE COMMAND are both programmed to "0"
(Conventional mode), then D0, D1, D2, D3, and D4 can be programmed independently to "1" for that drive to be set
automatically to Perpendicular mode. In this mode the following set of conditions also apply:
1. The GAP2 written to a perpendicular drive during a write operation will depend upon the programmed data rate.
2. The write pre-compensation given to a perpendicular mode drive will be 0ns.
3. For D0-D3 programmed to "0" for conventional mode drives any data written will be at the currently programmed
write pre-compensation.
Note: Bits D0-D3 can only be overwritten when OW is programmed as a "1".If either GAP or WGATE is a "1" then D0-
D3 are ignored.
Software and hardware (PCI) resets have the following effect on the PERPENDICULAR MODE COMMAND:
1. "Software" resets (via the DOR or DSR registers) will only clear GAP and WGATE bits to "0". D0-D3 are unaffected
and retain their previous value.
2. PCI resets will clear all bits
(GAP, WGATE and D0-D3) to "0", i.e all conventional mode.
Table 27 − Effects of WGATE and GAP Bits
PORTION OF
GAP 2
WRITTEN BY
WRITE DATA
OPERATION
FIELD
LENGTH OF
GAP2 FORMAT
WGATE GAP
MODE
Conventional
Perpendicular
(500 Kbps)
Reserved
0
0
0
1
22 Bytes
22 Bytes
0 Bytes
19 Bytes
1
1
0
1
22 Bytes
41 Bytes
0 Bytes
(Conventional)
Perpendicular
(1 Mbps)
38 Bytes
LOCK
In order to protect systems with long DMA latencies against older application software that can disable the FIFO the
LOCK Command has been added. This command should only be used by the FDC routines, and application software
SMSC DS – LPC47S45x
Page 61 of 259
Rev. 07/09/2001
DATASHEET
SMSC [ SMSC CORPORATION ]
